/**样式与颜色
 * api:
 *  fillStyle='red'
 *  strokeStyle ='red'
 *  globalAlpha = 0-1
 *  lineWidth = 1  线宽
 *  
 */

 /**
  * 渐变
  * api:
  *  createLinearGradient(x,y,x,y)
  */